Motor vehicle gearbox

ABSTRACT

The invention relates to a motor vehicle gearbox with two concentrically mounted input shafts (6,9), each driving an individual countershaft (12,15). The countershafts have gear wheels (16,18,19,41) in engagement with gear wheels (21,22,40) on an output shaft. The shafts are arranged in a V-configuration and one countershaft has a disengageable gear wheel (23) in engagement with a gear wheel (11) on the second countershaft to reverse the rotational direction of the latter for driving in reverse. One countershaft (12) has a central synchronizing device (30), by means of which the countershaft, which is drivingly coupled to the temporarily non-driven input shaft, can be accelerated up to a rotational speed determined by the gear speed selected.

This present invention relates to a motor vehicle gearbox, comprisingtwo concentrically mounted input shafts arranged to be drivenalternately, and two countershafts driven by the input shafts, saidcountershafts having gear wheels in engagement with gear wheels on anoutput shaft, at least one of the gear wheels on each countershaft beingrotatably mounted on its shaft and being lockable by means of engagingmeans to the shaft.

Double countershafts are used on one end in gearboxes in which it isdesired, with a given length of the gearbox, to obtain more gear ratiosthan what is practically possible in a conventional gearbox design withone countershaft, and on the other hand in so-called power shiftgearboxes, i.e. gearboxes with double inputs, each driven by anindividual clutch. In such gearboxes, the gear speeds are preselected,and shifting is effected thereafter by disengaging one clutch andengaging the other clutch. In both of these known types of gearboxes,the driving of the countershafts is arranged so that they are alwaysdriven simultaneously, and each engaging sleeve is coordinated with itsown synchronizer, i.e. the gearbox has a synchronization for each gear,which affects both the dimensions and weight of the gearbox.

In another gearbox type with double countershafts, which is known bye.g. GB A 2 110 324, a single input drives at the same time two gearwheels, which via individual clutches on the respective countershaft canbe locked to the shaft and establish a gear train between the inputshaft and output shaft via either countershaft. Shifting is effectedaccording to the above mentioned power shift pattern, synchronizationbeing achieved with the aid of a central synchronizing clutch on eachcountershaft at the output end of the gearbox. The synchronizing devicescomprise in addition to the clutches a total of six synchronizing gears,two of which are journalled on extra shafts.

The purpose of the present invention is to provide in a gearbox of thetype described by way of introduction and using the known principle ofcontrol synchronization, a basic design which permits more compact andlighter construction that what has been achieved previously and whichopens the way to completely new variants each of which having advantagesover the previously known designs and contributed together in particularto a very compact design of gearboxes with a large number of gearspeeds.

This is achieved according to the invention by virtue of the fact thatthe countershafts are coordinated with synchronizing means independentof said engaging means, by means of which synchronizing means thecountershaft which is drivingly coupled to the temporarily non-driveninput shaft, can be accelerated up to a rotational speed determined bythe gear speed selected.

Such a two-position central synchronization can be achieved with the aidof merely two synchronizing gears and with a synchronizing clutch ononly one countershaft. The central synchronization has six synchronizingfunctions in a six-speed gearbox, which means reduced weight and smallerdimensions. The design according to the invention results in particularin very short shafts, which is advantageous with regard to torquetransmission capacity and gear- and bearing-life.

If the output shaft is placed in a plane spaced from the plane of thecountershafts, i.e. the shafts are placed in a V-shape, thecountershafts can be provided with a pair of gear wheels in engagementwith each other, at least one of which is freely rotatably mounted onits shaft and is lookable by means of clutch means to the shaft toreverse the rotational direction of the second countershaft. In this wayone countershaft is used for the reversing function as well, and it ispossible thereby without an extra countershaft for reverse gear in asix-speed gearbox for example to obtain five speeds in reverse.

Further features and advantages of the invention will be evident fromthe following description with reference to an example shown in theaccompanying drawing, in which the FIGURE shows a longitudinal sectionthrough a six-speed gearbox.

In the FIGURE, 1 designates an engine flywheel, which via a multipledisc wet clutch (generally designated 2) drives a gearbox 3 according tothe invention. The clutch 2 is a double clutch of a type known per seand therefore need not be described more in detail here. The clutch unit4 to the left in the FIGURE is coupled via a sleeve element 5 to a firstinput shaft 6 in the gearbox, while the right-hand clutch unit 7 iscoupled via a sleeve element 8 to a second input shaft 9 in the form ofa hollow shaft concentrically mounted on the first shaft 6. The twoclutch units can in a known manner be alternately engaged or disengagedin order to alternately drive the input shaft 6 and 9. The multiple discwet clutch shown can be replaced by a double clutch of dry disc-type.

The first input shaft 6 is provided with a gear ring 10 in engagementwith a gear wheel 11 which is solidly fixed to a first countershaft 12.The second input shaft 9 is provided with a gear ring 13 in engagementwith a gear wheel 14 which is solidly fixed to a second countershaft 15.The gear ring 13 is larger than the ring 10, which means that the secondcountershaft 15 will rotate more rapidly than the first when the inputshafts rotate at the same rotational speed.

Countershafts 12 and 15 carry individual pairs of freely rotatablymounted gear wheels 16,17 and 18,19 respectively. Gear wheel 16,18 areboth in engagement with a gear wheel 21 solidly fixed to an output shaft20. Gear wheels 17,19 are in engagement with a gear wheel 22 fixed tothe output shaft. The shafts are arranged in V-shape to make it possiblewith an extra gear wheel 23 on countershaft 15, which gear wheel engagesthe gear wheel 11 on countershaft 12, to reverse the rotationaldirection of either countershaft for backing the vehicle. It is alsopossible to reverse the rotational direction of either countershaft bymeans of a gear wheel mounted on a separate shaft in the housing, saidgear wheel engaging the gear rings 10 and 23. This provides a freerselection of V-shapes and gear ratios and also enables the shafts to beplaced in the same plane. The gear wheels 16,17,18,19 and 23 arelockable to their shafts with the aid of axially displaceable engagingsleeves 24,25 and 26. A gear wheel 40 freely rotatable on the outputshaft 20 engages gear teeth 41 directly cut into the countershaft 15 andit is lockable to the shaft 20 by means of an engaging sleeve 42. Bycutting the gear teeth 41 directly into the countershaft 15 andarranging the gear wheel 40 lockable to the output shaft, the need iseliminated for needle bearings on the countershaft gear wheel, so thatit can be made with a very small diameter, which in turn makes a largegear ratio possible from the countershaft to the output shaft. With theaid of an engaging sleeve 27, the input shaft 6 and the output shaft 20can be locked together for direct drive.

All of these engaging means lack individual conventional synchronizingdevices.

Instead, according to the invention the first countershaft 12 iscoordinated with a central synchronizing device generally designated 30.This comprises a pair of gear wheels 32,33 freely rotatably mounted onan extension 31 of the countershaft 12, and an intermediate clutch disc34 which is joined to a sleeve 35 provided with axial grooves. Axialsplines 36 on the shaft portion 31 engage in the grooves in the sleeve35 so that the sleeve and the disc 34 are axially displaceable butnon-rotatable relative to the shaft 12. The sleeve 35 is connected toshift-controlling operating means (not shown in more detail here), e.g.a pneumatical hydraulic operating cylinder. The synchronizing gearwheels 32,33 are provided on their sides facing the disc 34 withfrictional surfaces 37,38. The left-hand gear wheel 32 engages a gearring 39 on the second input shaft 9. The gear ring 39 can have the samenumber of teeth as the gear ring 10 on the first input shaft, but inorder to prevent blocking when shifting, the gear rings 10 and 39 arepreferably made with teeth differing in number by one to two, forexample. The right-hand synchronizing gear wheel 33 engages the gearring 13 on the second input shaft and here there is preferably adifference of one or two teeth between the synchronizing gear wheel 33and the driven gear wheel 14 on the second countershaft.

In the FIGURE, the gearbox is shown in a neutral position with bothclutch units 4 and 7 disengaged. The first gear speed can be engaged bysliding the engaging sleeve 42 to the right, whereupon the gear wheel 40is locked to the output shaft 20. Thereafter clutch unit 7 is engagedwhile clutch unit 4 remains disengaged. When driving in the first gearspeed, the countershaft 12 remains stationary or substantiallystationary. When the second gear speed is to be engaged, which is doneby locking the gear wheel 16 to the countershaft 12 with the aid ofengaging sleeve 24, the shaft 12 must be accelerated up to a rotationalspeed which is lower than that of the shaft 15. This is done bysynchronizing the clutch disc 34 of the synchronizing device 30 to theleft against the gear wheel 32, which is thus locked to the shaft 12.

After the process described, which can be called presynchronization andwhich involves preselection of the second gear speed while driving inthe first gear speed, the actual shifting is effected by disengagingclutch unit 7 and engaging clutch unit 4. Presynchronization accountsfor approximately half of the synchronization work and since it occursduring normal driving it can be done relatively slowly which is anadvantage when dimensioning the components.

When preselecting the third gear speed, which is done by locking thegear wheel 18 to countershaft 15, the shaft 15 must be acceleratedalmost to the same rotational speed as shaft 12, since the gear wheel 18rotates at the same speed as gear wheel 16. This is done by displacingthe clutch disc 34 to the right against the gear wheel 33, which is thenlocked to the shaft 12 and drives the shaft 15 via the gear ring 13 andthe gear wheel 14. By seeing to it as in the case above that the shaft15 and the gear wheel 18 have approximately the same speed, the engagingsleeve 25 can be displaced into engagement with the gear wheel 18without a risk that engaging teeth will come into such a position thatshifting is blocked.

When preselecting the fourth gear speed, the countershaft 12 isaccelerated to essentially the rotational speed of the gear wheel 17,i.e. a rotational speed which is lower than that of the countershaft 15.This is done by the synchronizing-disc 34 being moved to the left in theFIGURE for engaging the synchronizing gear wheel 32, whereafter theactual shifting is effected by disengaging clutch unit 7 and engagingclutch unit 4. Continued shifting up to the fifth and sixth gear speedis done in a corresponding manner by alternatingly locking thesynchronizing gear wheels 32,33 to countershaft 12.

For driving and release the gear wheel 23 is locked with the aid ofengaging sleeve 26. Depending on which of the clutches 4,7 is engaged,the rotational direction of either countershaft 12 or countershaft 15can be reversed, and a total of five reverse gears are obtained bylocking one of gear wheels 16,17,19,18,40. By direct coupling by meansof engaging sleeve 27, a sixth reverse gear can be obtained.

Instead of the mechanical central synchronization described here, it ispossible within the scope of the invention to have an electronicvariation, e.g. one in which the intermediate shafts are coupled toindividual electric motors which are controlled by a microcomputer,which selects the correct rotational speed for each countershaft forgear speed preselection. Such a variant provides greater freedom inselecting the increments between the gear speeds but on the other handis somewhat more complicated and less reliable. Furthermore, it ispossible to use the free clutch and give it a short engagement toprovide the free countershaft with a suitable speed. The invention canof course also be used in gearboxes with more or fewer gear speeds thanthat described above.

We claim:
 1. A motor vehicle gearbox, comprising first and secondconcentrically mounted input shafts, said input shafts arranged to bedriven alternately such that one said input shaft comprises atemporarily non-driven input shaft, an output shaft, and first andsecond countershafts driven by said first and second input shafts,respectively, said countershafts .Iadd.having spaced parallel axes and.Iaddend.having gear wheels in engagement with gear wheels on saidoutput shaft, .Iadd.a gear wheel on each countershaft being in drivingengagement with a common gear wheel on said output shaft, .Iaddend.atleast one of the gear wheels on each countershaft being rotatablymounted thereon and being lockable by means of engaging means to saidcountershaft, and each input shaft being in driving engagement with acorresponding countershaft, said first and second countershafts beingcoordinated with synchronizing means shiftable independently of saidengaging means, by means of which synchronizing means each countershaft,which is drivingly coupled to said respective temporarily non-driveninput shaft, can be accelerated up to a rotational speed determined by agear speed selected.
 2. The motor vehicle gearbox of claim 1, whereinsaid synchronizing means is arranged to adapt the rotational speed ofone of said countershaft to approximately that of the gear wheel to beengaged.
 3. The motor vehicle gearbox of claim 2, wherein saidsynchronizing means comprises a pair of gear wheels rotatably mounted onone of said countershafts, and friction means by which one of said gearwheels can be drivingly connected to said one countershaft, said gearwheels being in driving engagement with gear rings on said correspondinginput shaft.
 4. The motor vehicle gearbox of claim 3, wherein said gearwheels serving as synchronizing means include opposing frictionalsurfaces and an intermediate friction plate axially displaceable butnon-rotatably joined to said one countershaft and connected to shiftingcontrol means.
 5. The motor vehicle gearbox of claim 1, wherein saidoutput shaft includes gear wheels which engage with gear wheels of equaldimension on said first and second countershafts.
 6. The motor vehiclegearbox of claim 1, wherein said output shaft lies in a plane spacedfrom a plane of the said first and second countershafts, and saidcountershafts including a pair of gear wheels drivingly connected toeach other, of which gear wheels at least one is freely rotatablymounted on said second countershaft and is lockable by means of engagingmeans to said second countershaft to reverse the rotational direction ofsaid output shaft.